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Discussion Starter #1
Hi everyone,

I'm replacing the spark plugs on my 1999 SLK230 and one of them is stuck pretty good. I was wondering if anyone knows whether the holes are helicoiled so I know how much I can crank at this thing without worrying about stripping the threads? Thanks!
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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moving to r170 section
 

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Administrator 2009 SLK 55 AMG/Founding Member 2006
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I'm warning you to be very careful trying to remove a stuck spark plug. If you strip out the threads, you'll have world of expensive misery facing you.

The proper procedure is to find a solvent like PB Blaster or Gunk Liquid Wrench to loosen up the plug. If there is a well around the plug, fill it up with either or both. Let it soak in. It may take several days, but the crud around the threads will eventually let go.

When loosening the plug, just try to move it at most just a little bit then let it soak some more. The name of the game is patience, and you will eventually get the plug out. When installing the new plug, use an anti-seize grease (just a little).
 

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Discussion Starter #5
Yeah, that's what I'm worried about... not worth risking stripping the threads. I figured if they were helicoiled I would have more leeway in cranking at it though. I did apply some solvent but only had half an hour or so to let it set at the time, so maybe I'll take another crack at it in a couple days and apply some more and see if I get anywhere. Thanks for the suggestion!

Does anyone else have any thoughts or suggestions on this?
 

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The head is aluminum, and the threads are tapped into this material. Over time, the plug and head can form a very tight union almost like a weld, so you have to be careful removing plugs. If you use a bit of anti-seize, you'll prevent the problem.

If you strip out the head, you'll have to remove it to get a helicoil put in. Also it may not be possible to do it to begin with. Imagine what a new head will cost or the chance of finding one in the bone yard? Also a used head will likely have to be reconditioned - more moolah!

Frankly, I know a way to solve the problem. Remove any traces of your efforts and drop it off at a MB service center for a new set of plugs. If they strip it, it is their problem. They won't because they have the tools and techniques to handle it.
 

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^^ What she said - I've done that in the past with other cars - I'm willing to pay to make it someone elses problem!
 

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i had the same problem

I had the same problem...was total Biatch to get two of them out... I had to use penetrating oil, (I like the spray can stuff) sat overnight and then a long breaker bar took care of it.

I had to wiggle it both ways but finally got it. I suspect it had never been changed in 11 years and 111k.

But I do like the route of dropping it at the MB dealer.
 

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That's probably why the service interval is 5 years or 100,000 miles. I'm not so sure that taking it to a dealer or other service center will alleviate you from the cost if things don't go well. If the shop can't get them out and strip the threads instead of you doing it, I'm not so sure they are responsible for the additional work/cost involved with making things right. It's not necessarily their fault. I know when a similar thing happens with glow plugs on Mercedes diesels, it's the customer and not the shop that pays for it.

Len
 

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Mercedes Service Centers are well aware of problems with removing plugs in aluminum heads. Remember that the service interval is 60K miles! With that mileage interval, many cars will never see a plug change, since some owners don't rack up a lot of mileage.

Also the tech recognizes instantly when a reasonable amount of effort won't budge the plug. About the only way the threads get stripped out is when an amature tries to remove them. The tech will use heat, penetrating oil, or recommended procedures formulated by Mercedes. It is unlikely he'll fail.

Suppose he does? Then it is likely your efforts would have too. And certainly the Benz Service Center knows how to fix the problem. Unfortunately, the more time devoted to the problem the more costly it is going to get! In the US, the labor rates on a Ford aren't much different than a Benz.

Anyway, I have dealt with this problem, and I have found patience is the key to success. For those flush with cash, I recommend the service center!
 

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Discussion Starter #11
Sounds like the service center is the way I'll probably go, as long as they aren't too outrageous. Guess I'll give them a call this weekend for an estimate and go from there.
 
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